1. Field of Invention
The present invention relates to a special-type high-voltage measuring current transformer.
2. Description of Related Arts
A plurality of lines in substations often work in a weak current and weak magnetic field condition where the conventional high-voltage transformers are unable to measure, causing various types of trade meters, monitoring instruments and monitoring microcomputers unable to work normally.
The weak current is often in thousandths of a rated current of the transformer, so as to cause the following three problems.
a) The conventional high-voltage transformers have measuring performance only for hundredths of the rated current, despite of a large error. For example, the error of the 0.2Ss class transformer reaches ±0.2% for more than two tenths of the rated current and the error of the 0.2Ss class transformer for the hundredths of the rated current is ±0.3% to ±0.8%.
b) It is impossible to change the measuring performance in the weak magnetic field by changing the transformation ratio, not to mention to change the measurement precision. For example, when the transformer is changed from 600/5 A to 100/5 A, the weak current of 1.2 A is changed from 2‰IN to 1.2% IN.
c) As the primary equipment running in high-voltage lines, the high-voltage transformer is not allowed to be changed from 600/5 A to 100/5 A for a protection purpose.